This invention relates generally to the field of methods and processing systems for treatment of large volumes of citrus peel or similar waste products to be converted into useable products and to extract desirable components for distinct applications. More particularly, the invention is such a method and system for the processing of citrus peel, pulp waste and/or by-products which are produced during a juice extraction process, in order to recover useful liquid and solid components for future use, in a manner whereby the useful recovered components, such as d-limonene or peel oil, peel juice or syrup molasses, pectin pomace, citrus peel flour and many other liquid and dry masses, are of food-grade quality, and further such that the wastewater effluent produced by the system is sufficiently purified of suspended solids, soluble solids, sugars and oils, and in view of the fact that no chemical agents are added in the process, the waste water can be safely discharged into standard sewer systems due to its low biological oxygen demand (BOD), and where processing time, energy needs and costs are greatly minimized when compared to existing processes.
Nearly 50 billion pounds of citrus are processed each year, mainly to extract drinkable juices for the consumer market. The extraction of the juice creates a large amount of waste by-product in the form of orange peel, seeds, rag (the membranes between the citrus segments) and pulp. In the U.S., the waste organic material cannot be dumped into landfills, but instead must be converted into a useable product. The waste is primarily converted into citrus pulp pellets (CPP) for cattle feed, since the waste peel and other components provide filler and a protein source, although at only about 6% protein content it is not a high protein source food. Natural citrus peel oil contained within the peel is a marketable by-product, and current processing removes approximately 25–40 percent of the total available quantity from the peel by extractors compressing the fruit sphere prior to removal of the juice and further processing. The oil is then further processed and refined and currently sells at about $1.00 per pound in the form of cold press peel oil. The current technology for processing the waste peel operates at a loss—the costs are more to process the material than can be regained by selling the resulting products as a non-food grade material due to toxic chemical dewatering methodology.
The current state of the art for processing citrus peel is a system which squeezes the peel to remove some of the citrus oil, slices the fruit in half, reams or presses the halves to remove the juice and pulp, and ejects the waste peel, rag, seed, etc. to a conveyor for transport to a peel processing plant. The peel is then delivered into fixed rotor blade hammer mills which rotate and thrash the peel in a very inefficient manner relative to particle size and rate control, with resulting particles ranging from one square inch pieces up to entire fruit halves. The thrashed peel is then placed into mixing augers where lime (calcium oxide) is added to dehydrate the peel, the lime contacts free water forming a basic anhydride reaction, producing calcium hydroxide (CaOH), which is toxic. Alternatively, the lime is sometimes applied prior to the hammer mill step. The result is an orange peel cake material containing about 80% residual water. The addition of the lime renders any subsequent products unsuitable for human consumption. The thrashed waste material is pressed, which removes approximately 10 to 15% of the free water along with some residual oil, which is called pressed liquor. The liquor is pumped to waste heat evaporators where water is evaporated to produce a low brix molasses of about 50 brix sugar content. This molasses is sprayed onto the cattle feed pellets produced from the peel particles to enhance the flavor and subsequent ingestion by beef and dairy cattle. The pressed peel particles are then passed through large, gas-fired, single-pass or multi-pass, low rpm (3–10), rotary dryers, typically about 18 feet in diameter by 80 feet in length, where predominantly gas fired air is heated to about 1500 degrees F. and raises the particle temperature to a range of about 290 to 700 degrees F. over the course of about 45 minutes. The high heat of the air in the dryer actually combusts or flashes off most of the volatile liquids and gases in the peel, emitting VOC's and associated hydrocarbons into the exhaust air to atmosphere. Burnt gases, liquids and solids coat and foul the interior ductwork and dryer contact surfaces, often leading to fires within the equipment and fan blade failures. Since the exhaust air contains a large amount of contaminants such as particulate matter, VOC's, oil, moisture, etc.; the air flow must pass through scrubbers to remove a significant portion of the contaminants. The scrubbers typically utilize water sprays, which drastically reduces the potentially recoverable heat energy of the exhaust air by about two thirds. This scrubbed air is then passed to heat recovery equipment, where the lowered heat value (about 180 degrees F.) is then used as the heat source in waste heat evaporators for the production of molasses. Currently, exhaust air must be scrubbed prior to passage through the heat recovery equipment to prevent plate surface fouling, which reduces performance and may cause failure. The dryer-discharged, dried peel matter has a moisture content of about 10 to 15% and is then pelletized into citrus peel pellets, ranging from about ⅜ to ¼ inches in diameter and from about ¼ to one and one quarter inches in length. The pellets are then sold as cattle feed at a price of about $40/ton, even though the processing costs to produce the pellets ranges from about $60–70/ton. The current systems utilize oil or natural gas combustion heating, are processes utilizing equipment which are not able to be cleaned on-line except by shutting down the process, are unable to recoup most of the exhaust heat energy, produce contaminated air which must be scrubbed prior to reuse or exhaust to the atmosphere, cannot remove any of the 85–90% residual citrus oil, and cannot produce a food grade product for human consumption due to the addition of lime during the process.
An improved method and system to those described above is disclosed in my U.S. Pat. No. 6,151,799, issued Nov. 28, 2000, wherein the disclosed invention comprises means to convey the waste citrus peel to a pulping means, preferably comprising a storage conveyor, an elevator conveyor, a metering tube and continuous weigh belt such that the delivery of the peel occurs in a controlled, uniform manner rather than by batch delivery, means to elevate the temperature of the waste peel, preferably comprising a live steam jacket incorporated into the metering tube, pulping means to fragment the waste peel into particles of small size thereby creating a slurry of water and citrus oil, preferably comprising a high-shear rotary disintegrator, means to separate liquid from the waste particles, preferably comprising a vibratory shaker table with hot water spraying system and a press, means to subsequently dry the solid particles, preferably comprising a defragmentor, a fluidized, dynamic bed, low temperature, high air volume circulation dryer, heat recovery means for reuse of the dryer exhaust air, preferably comprising an exhaust air particulate screener and heat exchanger unit, the heat recovery means acting to preheat air for the dryer and/or to evaporate water from press liquor to create molasses, and centrifuge means to remove water and solids from the oil/liquid emulsion from the shaker table to create marketable citrus oil. This system, however, suffers from certain inadequacies and does not fully address the issue of wastewater composition.
It is an object of this invention to provide a system and method which addresses the drawbacks from the current waste peel processing and drying systems. It is an object of this invention to provide a waste peel collection, processing and drying system and methodology to recover useful liquid and solid components for future use, in a manner whereby the useful recovered components, such as d-limonene or peel oil, peel juice or syrup molasses, pectin pomace, citrus peel flour and many other liquid and dry masses, are of food-grade quality, and further, such that the wastewater stream produced by the system is sufficiently purified of suspended solids, soluble solids, sugars and oils, and in view of the fact that no chemical agents are added in the process, the waste water can be also used as a consumable liquid commodity and of course safely discharged into standard sewer systems due to its low biological oxygen demand (BOD).